Focus detection system and lighting device therefor

ABSTRACT

A lighting device such as an electronic flash device attachable to a camera body includes first and second light projecting optical systems which project first and second light fluxes for illuminating an object to aid focus detection by a focus detection device. The second light flux spreads at a larger solid angle than the first light flux and illuminates a first distance zone which extends to a closer distance side while covering the whole of a second distance zone illuminated by the first light flux. An optical wedge disposed in the second light projecting optical system deflects a part of the second light flux towards the closer distance side of the first distance zone. Another lighting device includes a single light projecting optical system but it also includes an optical wedge for deflecting a part of a light flux projected by the light projecting optical system to widen a distance zone illuminated by the light flux towards a closer distance. The optical wedge also serves to produce a difference in intensity distribution of the light flux such that the light flux has higher intensity at a part thereof for illuminating a farther distance side of the distance zone than at a part thereof for illuminating a closer distance side of the distance zone. A light source of the light projecting optical system(s) is provided with a conical light reflecter surrounding a light emitting diode to reflect light emitted from side surfaces of the light emitting diode forward.

This application is a continuation of application Ser. No. 084,938,filed Aug. 13, 1987, now abandoned, which is a divisional of Ser. No.940,190, filed Dec. 9, 1986, now U.S. Pat. No. 4,690,538, which in turnis a continuation of Ser. No. 807,642, filed Dec. 11, 1985, nowabandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a T.T.L. (through the lens) focusdetection system utilizing an auxiliary light to help focus detectionand a lighting device for projecting such an auxiliary light.

2. Description of the Prior Art

There have been proposed a variety of T.T.L. focus detection systemswhich detect focusing condition of an objective lens based on the lightwhich has passed through the objective lens. The typical systems are thephase difference detection system disclosed in Japanese Patent Laid OpenPublication Nos. 52-95221 and 54-159259 or contrast detection systemdisclosed in Japanese Patent Liad Open Publication No. 55-155308. Ingeneral, a T.T.L. focus detection system has such a disadvantage that itcan hardly or cannot carry out focus detection when the object is darkor the contrast of the object is low. In such a case, a lighting devicewhich projects an auxiliary light toward the object is used in order tohelp the focus detection. For example, such examples are disclosed inthe specifications of U.S. Pat. No. 4,150,888 and in Japanese PatentLaid Open Publication No. 57-73709.

However, various problems are left unsolved in putting into practicaluse such focus detection system utilizing an auxiliary light emittedfrom a lighting device as described above. One of the most seriousproblems among them is how to effectively light the object scene withinthe range from the near to far distance. Particularly, a lensexchangeable camera like a single-lens reflex camera which allowsinterchange of a variety of lenses is required to have a high focusdetection accuracy and also to be capable of carrying out focusdetection with respect to an object within a wider range of near to fardistance with a variety of lenses from super wide-angle to supertelephoto lenses in use.

Therefore, a lighting device used for such a lens exchangeable camera isalso required to be capable of lighting wider distance range from thenear to far distance while covering the focus detection area spreadingat a solid angle dependent on the angle of the field of a lens attachedto the camera. In case the lighting distance is to be increased, it ispossible to raise the light condensing capability of a light projectingoptical system to make the spread of the projected light small. However,in this case, the lighting range is narrowed and it is no longerpossible to light the objects within a range from the near to fardistances at the same time unless the light is projected from the cameraalong the optical axis through the objective lens. On the contrary, ifthe light condensing capability of the light projecting optical systemis lowered and the spread of the projected light is widened, thelighting range can be widened but lighting distance is shortened.Moreover, if a power of light source of the light projecting opticalsystem is increased, the lighting range can be widened and the lightingdistance can also be elongated. However, this is not desirable ingeneral because a light source having a large capacity is required andpower consumption becomes large.

The lighting device disclosed in the specification of U.S. Pat. No.4,150,888 is provided with a light projecting optical system which ispivoted in conjunction with focusing movement of an objective lens sothat the angle of the light projection axis relative to the optical axisof the objective lens changes. With such a construction, objects withina range of near to far distance can be lighted in accordance with thefocusing movement of the objective lens and the lighting distance can beextened by raising the condensing capability of the light projectingoptical system. However, the lighting range is narrowed and, if theobjective lens is largely deviated from a proper focus position withrespect to a main object, the main object cannot be lighted by thelight, resulting in failure of focus dectection. In addition, as thelight projecting optical system should be pivoted as described above, amechanical interlocking system which interlocks the light projectingoptical system with the focusing movement of the objective lens isessential. Therefore, the lighting device is complicated inconstruction. Moreover it is difficult to provide a lens interchangeablecamera with such an interlocking mechanism.

On the other hand, in the case of the lighting device disclosed inJapanese Patent Laid Open Publication No. 57-73709, a light projectingoptical system is provided on the lens barrel of an exchangeable lensand this optical system is pivoted in conjunction with the focusingmovement of the objective lens of the exchangeable lens. Such a lightingdevice is free from the disadvantage of difficulty in application to alens exchangeable camera but still suffers from the other disadvantagesof the lighting device disclosed in the specification of U.S. Pat. No.4,150,888.

Moreover, such a lighting device suffers from another disadvantage thateach exchangeable lens becomes very expensive since the light projectingoptical system must be provided on the lens barrel of each escahngeablelens.

SUMMARY OF THE INVENTION

It is accordingly an object of the present invention to provide a T.T.L.focus detection system for a camera utilizing an improved lightingdevice which can eliminate the above described disadvantages of theprior arts.

Another object of the present invention is to provide a lighting deviceconstituted as an accessory attachable to the camera and adapted toilluminate a wider distance range within a focus detection area with ahigh lighting efficiency.

A focus detection system of the present invention may have two forms,one of which includes first and second light projecting optical systemsand the other of which includes a single light projecting opticalsystem. In the case of the focus detection system of the presentinvention including the first and second light projecting opticalsystems, the first light projecting optical system projects a first fluxof light which illuminates a first distance zone within a focusdetection area and the second light projecting optical system projects asecond flux of light which illuminates a second distance zone within thefocus detection area. Here, the focus detection area spreads at apredetermined solid angle centering at the optical axis of an objectivelens of the camera and depending upon the objective lens. The seconddistance zone is set wider than the first distance zone so as to coverthe whole of the first distance zone at a farther distance side thereofand so as to extend beyond the first distance zone at a closer distanceside thereof. Accordingly, the farther distance side of the seconddistance zone within the focus detection area is illuminated or lightedby the first and second fluxes of light projected by the first andsecond light projecting optical systems and the closer distance side ofthe second distance zone within the focus detection area is illuminatedor lighted by the flux of light projected by the second light projectingoptical system. Namely, the lights illuminating the farther distanceside are intensified by the overlap of the first and second fluxes oflight to raise a lighting efficiency, and therefore it is made possibleto widen the distance range for focus detection i.e., the seconddistance zone which is as a whole illuminated or lighted by the secondflux of light projected by the second light projecting optical system.The close distance side is illuminated or lighted only by the secondflux of light but this does not matter because of the shorter distance.Due to the increased lighting efficiency it becomes unnecessary toprovide an interlocking mechanism interlocking any of the first andsecond light projecting optical system with focusing movement of theobjective lens and therefore the system of the present invention issuited for a lens exchangeable type camera.

In the case of the focus detection system of the present inventionincluding the single light projecting optical system, the lightprojecting optical system projects a flux of light which crosses thefocus detection area at a predetermined angle and means is provided toproduce a difference in intensity distribution of the flux of light sothat the flux of light has a higher intensity at a part thereof forilluminating a farther distance zone within the focus detection areathan at a part thereof for illuminating a closer distance zone withinthe focus detection area. Such difference in intensity distribution ofthe flux of light may be produced by deflecting a part of the flux oflight towards the closer distance zone. It is also made possible by thisarrangement to widen the distance range for focus detection without useof a interlocking mechanism interlocking the light projection opticalsystem with focusing movement of the objective lens.

According to the present invention, the first and second lightprojecting optical systems can be incorporated in a lighting devicewhich is attachable to the camera. Similarly, a lighting deviceattachable to the camera may incorporate the single light projectingoptical system and the difference producing means. Such a lightingdevice may be an electronic flash device which emits flash light forflash photography in addition to the first and second fluxes of light orthe flux of light for focus detection.

The novel features which are believed to be characteristic of theinvention, both as to organization and method of operation, togetherwith further objects and advantages thereof, will be better understoodfrom the accompanying drawings in which several preferred embodiments ofthe invention are illustrated by way of example. It is to be understood,however, that the drawings are for the purpose of illustration anddescription only and are not intended as a definition of the limits ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows outline of a focus detection system utilizing a lightingdevice according to a first embodiment of the present invention.

FIG. 2 illustrates a focus detection optical system of the focusdetection system of FIG. 1.

FIG. 3 is a development view showing the principle of focus detection bythe focus detection optical system of FIG. 2.

FIG. 4 is a plan view of first and second light projecting opticalsystems of the lighting device of the first embodiment.

FIGS. 5 and 6 are a plan view and a side elevation view indicatedpositional relationship between the light fluxes projected from thefirst and second light projection optical systems of FIG. 4 and thefocus detection area, respectively.

FIG. 7 is a graph indicating relationship between the angle formed by alight projecting optical axis and the optical axis of the objective lensand the lighting distance range.

FIGS. 8A and 8B respectively illustrate overlapping conditions of thelight fluxes projected from the first and second light projectingoptical systems at the distacne of 1 m and 5 m and positionalrelationship between the overlapping conditions and the focus detectionarea.

FIG. 9 is a perspective view of first and second light projectingoptical systems of a lighting device according to a second embodiment ofthe present invention.

FIG. 10 is a side elevation view of the second light projecting opticalsystem of FIG. 9.

FIGS. 11 and 12 are a plan view and a side elevation view indicatingpositional relationship between the light fluxes projected from thefirst and second light projecting optical systems of FIG. 9 and thefocus detection area, respectively.

FIG. 13 illustrates the overlapping condition of the light fluxesprojected from the first and second light projecting optical systems atthe distance of 2 m in the second embodiment and positional relationshipbetween such condition and the focus detection area.

FIGS. 14 and 15 are side elevation views of second light projectingoptical system according to first and second modifications of the firstand second embodiments, respectively.

FIG. 16 is a side elevation view of a light projecting optical systemaccording to a third embodiment of the present invention.

FIG. 17 is a side elevation view of the light fluxes projected from thelight projecting optical system of FIG. 16.

FIG. 18 is a graph illustrating the relationship between relativeluminosity (stimulus to human eyes) and wavelength.

FIG. 19 is a graph of spectral reflectivity of green, blue-gray andwhite substances.

FIG. 20 is a plan view illustrating an example of projective patternfilm.

FIG. 21 illustrates a projective pattern image consisting of a singleopaque part projected on a plain object, wherein the image is viewedtogether with a field frame from the focus detecting surface where theimage sensing device is located.

FIG. 22 is a plan view illustrating another projective pattern film.

FIG. 23 illustrates the range of overlapping of the two projectivepattern images in the case where the projective pattern film is arrangedas shown in FIG. 4 within the first and second light projecting opticalsystems.

FIG. 24 illustrates the position of the projective pattern relative theoptical axis of the projection lens in FIG. 23.

FIGS. 25A and 25B ar a plan view and a side elevation view of the firstand second projection lenses integrated as a composite type projectionlens.

FIG. 26 is a perspective view of first and second light projectingoptical systems of a lighting device according to a fourth embodiment ofthe present invention.

FIG. 27 is a side elevational view indicating positional relationshipbetween the light fluxes projected by the first and second lightprojecting optical system of FIG. 26 and the focus detection area.

FIG. 28 is a cross-sectional view of the light source devices 207 and208 of FIG. 26.

FIG. 29 is a schematic diagram illustrating pencils of light emittedfrom the front surface of the light emitting diode 234 as the lightsource of the light source devices 207 and 208.

FIG. 30 is a graph illustrating relationship between change in the totalquantity of the light projected by the projection lens and change in l/Rshown in FIG. 29.

FIGS. 31 to 35 are schematic diagrams illustrating pencils of lightemitted from the side surfaces of the light emitting diode 234, whereinthe light reflective surface of the light reflecting member 232 of FIG.28 has an angle of inclination of 30° in FIG. 31, 35° in FIG. 32, 44° inFIG. 33, 55° in FIG. 34 and 65° in FIG. 35, respectively.

FIGS. 36 and 37 are graphs illustrating relationship between change inthe total quantity of the light projected by the projection lens andchange in the angle of inclination of the light reflective surface ofthe concave light reflecting member 232 of FIG. 28, in the case of theprojection lens of F No.=1.2 and F No.=1.7, respectively.

FIG. 38 is a graph illustrating relationship between change in the totalquantity of the light projected by the projection lens and change in thedistance from the vertex of the spherical molded portion 207a or 208a tothe light emitting diode.

FIGS. 39A and 39B are schematic diagrams illustrating the width of thelight flux emitted from the side surfaces of the light emitting diode234 in the case of the spherical molded portion 207a or 208A havingradius of curvature R=0.8 mm and R=1.0 mm, respectively.

FIG. 40 is a graph illustrating change in relative luminosity within thefocus detection area due to change in the radius of curvature R of thespherical molded portion.

FIG. 41 is a perspective view of first and second light projectingoptical systems of a lighting device according to a fifth embodiment ofthe present invention.

FIG. 42 is a side elevational view of one of the first and second lightprojecting optical systems of FIG. 41.

FIG. 43 is an enlarged schematic diagram of essential parts of the lightsource device of FIG. 42.

FIG. 44 is a schematic diagram of a projective pattern image formed bythe light source device of FIG. 42.

FIGS. 45 and 46 are enlarged schematic diagrams of essential parts offirst and second modifications of the light source device of FIG. 42,respectively.

FIG. 47 is a front view of the light source device according to thesecond modification of FIG. 46.

FIG. 48 is an enlarged schematic diagram of essential parts of a thirdmodification of the light source device of FIG. 42.

FIG. 49 is a front view of the light source device according to thethird modification of FIG. 48.

FIGS. 50A, 50B and 50C schematically illustrate overlapping conditionsof a light flux projected by a light projecting optical system at thedistances L_(MIN), L and L_(MAX) shown in FIG. 51 and the focusdetection area, respectively.

FIG. 51 is a side elevational view indicating positional relationshipbetween the light flux projected by a light projecting optical systemand the focus detection area, wherein B represents separation of a lightsource included in the light projecting optical system from the opticalaxis 14X of the objective lens.

FIG. 52 is a side elevational view of a light projecting optical systemof a lighting device according to a sixth embodiment of the presentinvention.

FIG. 53 is a side elevational view of the light flux projected by thelight projecting optical system of FIG. 52.

FIG. 54 is a cross-section of the light flux at I--I in FIG. 53.

FIG. 55 is a side elevational view of the light projecting opticalsystem same as that of FIG. 52, presented to explain how the light fluxis deflected by the prism 419 in front of the projection lens 417.

FIG. 56 is front view of the projection lens 417 showing theconfiguration of the prism 419 in front of the projection lens.

FIG. 57 is the same view as FIG. 55, wherein the prism 419 is arrangedat a position closer to the projection optical axis of the lightprojecting optical system than in FIG. 55.

FIGS. 58A, 58B and 58C are cross-sections of the light flux deflected bythe prism with the prism arranged at different position relative to theprojection optical axis.

FIG. 59A is a graph illustrating change in the range R_(min) -R_(max) ofthe light flux emitted to pass through the prism due to change in thewidth d₀ of the prism.

FIG. 59B is a side elevational view of the light projecting opticalsystem same as that of FIG. 52, presented to define the various factorsshown in FIG. 59A.

FIG. 60A is a graph illustrating change in the angle of deflection θ dueto change in the vertex angle δ of the prism.

FIG. 60B is a diagram to define the angle of deflection θ and the vertexangle δ of the prism.

FIG. 61 is a side elevational view of a light projecting optical systemof a lighting device according to a seventh embodiment of the presentinvention,

FIG. 62 is a side elevational view illustrating the positionalrelationship between the light flux projected by the light projectingoptical system of FIG. 61 and the focus detection area.

FIG. 63 is a front view of the projection lens 421 showing theconfigurations of the prism 423 and 424 in front of the projection lens.

FIG. 64 is a cross section of the light flux at II--II in FIG. 62.

FIG. 65 is a front view of a projection lens 434 of a lighting deviceaccording to an eighth embodiment of the present invention, shwoning theconfiguration of prisms 435, 436 and 437 in front of the projectionlens.

FIG. 66 is a side elevational view of a light projecting optical systemof a lighting device according to a ninth embodiment of the presentinvention.

FIG. 67 is a side elevational view of a light projecting optical systemaccording to a tenth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of the present invention is described at first withreference to FIGS. 1 to 6. The lighting device of the first embodimenthas two light projecting optical systems and is applied to an electronicflash device for taking a picture with flash. In FIG. 1, C represents alens exchangeable type camera constituted as a single-lens reflex camerahaving a main mirror Mi; EL and S represent respectively an exchangeablelens and a lighting device attached to the camera. The lighting device Sis mounted at the leg 4 on an accessory shoe 2 provided at the uppersurface of the camera C and provided with a known flash tube 6 forproducing flash light and first and second light projecting systemsincluding light source devices 7 and 8 described later and a pair ofprojection lenses 9 and 10 etc. The lighting device S is also providedwith a known circuit for flashing the flash tube 6, constituted by avoltage boosting circuit, a main capacitor and a trigger circuit, etc.and a circuit for energizing the light source devices 7 and 8. Thecircuit for energizing the light source devices 7 and 8 operates toenergize the light source devices 7 and 8 as required during focusdetection operation of the camera prior to exposure operation anddetails of the operation thereof are not described here because it isnot related to the subject matter of the present invention, the camera Chas a sub-mirror M₂ in addition to the main mirror M₁. The light from anobject having passed through the objective lens 14 of the exchangeablelens EL passes through a light transmitting part of the main mirror M₁to be reflected by the sub-mirror M₂ downward and then to enter a focusdetection device F.

FIGS. 2 and 3 illustrate an example of the optical system of the cameraC shown in FIG. 1 and the focus detection optical system provided in thefocus detection device F. In FIG. 2, 16 represents a field frame formedon a body of the device F for restricting the focus detection area. 18represents a condenser lens; 20 a light path folding mirror; 21 and 22 apair of reimaging lenses; 24 a self scanning image sensing deviceconsisting of charge accumulation type i.e., (light integration type)image sensing device such as a CCD, for example. FIG. 3 which is adevelopment view of the focus detection optical system consisting ofthese optical members shows the principle of focus detection of thephase difference detection type. 26 represent a predetermined imagingsurface of the objective lens 14 which is equivalent to a film surface28 of the camera. 30 represents a conjugate surface conjugate with theimaging surface 26 with respect to the reimaging optical systemconsisting of the condenser lens 18 and the pair of reimaging lenses 21and 22. A front focus image A, an in-focus image B and a rear focusimage C formed by the objective lens 14 are respectively re-imaged asthe first and second images A₁ ' and A₂ ', B₁ ' and B₂ ', and C₁ ' andC₂ ' by the condenser lens 18 and the pair of reimaging lens 22. Thepositional relationship between the first and second images changesdepending on the focus condition of the objective lens with respect tothe object within the focus detection area. As a result, the focuscondition of the objective lens can be detected by locating the imagesensing device 24 on or at the vicinity of the surface 30 andcalculating the distance between the first and second images on thebasis of outputs of the image sensing device 24. In FIG. 3, 14Xrepresents the optical axis of the objective lens 14 and 34 representsan aperture mask which forms a pair of aperture openings just in frontof the remaining lenses 21 and 22.

FIG. 4 is a plan view practically illustrating the light projectingoptical systems of the lighting device of FIG. 1. The projection lenses9 and 10 are disposed with an interval of D between the center thereof.The light source devices 7 and 8 respectively incorporate light emittingdiodes (not shown). These devices 7 and 8 are arranged at a position alittle backward (in the left side of the figure) from the point of focusof the projection lenses 9 and 10, respectively, so that their centersare respectively deviated by d from the optical axes of the projectionlenses 9 and 10. Formed on these devices are spherical light condensingportions 7a and 8a having radius of curvature R₁ and R₂ (R₁ <R₂) andwidth of φ_(A) and φ_(B), respectively. Moreover, the projection patternfilms 11 and 12 are accurately positioned substantially at the point offocus of the projection lenses 9 and 10 just in front of the sphericalportions 7a and 8a, so that the patterns described later are notdeviated from each other. The spherical portions 7a and 8a of the lightsource devices 7 and 8 are condensers for collecting the light fluxesemitted from the light emitting diodes to the effective diameters of theprojection lenses 9 and 10. But, since R₁ <R₂, the light flux projectedby the projection lens 10 spreads at a wider solid angle than the lightflux projected from the projection lens 9. Namely, the first lightprojecting optical system constituted by the light source device 7 andthe projection lens 9 has a higher light condensing (collecting)capability than the second light projecting optical system constitutedby the light source device 8 and the projection lens 10.

In FIGS. 5 and 6 which illustrate how the light fluxes projected fromthe first and second light projecting optical systems spread, the solidline indicates the light flux projected from the first light projectingoptical system and the broken line the light flux projected from thesecond light projecting optical system. The area indicated by thehatching indicates the spread of focus detection area of the focusdetection device F which is restricted by the field frame 16. As shownin FIGS. 4 and 5, the projection optical axes 7x and 8x of the first andsecond light projecting optical systems together cross the optical axis14x of the objective lens at the predetermined distance L=3 m in thehorizontal direction while crossing the optical axis 14x at thedistances 3 m and 1.8 m in the vertical direction respectively as shownin FIG. 6. Namely, the two projection optical axes 7x and 8x areextending in such a fashion that they are twisted and such twist ofprojection optical axes can be realized by giving difference todistances in the vertical direction from the optical axes of lightsource devices 7 and 8 to the optical axes of the projection lenses 9and 10, or by giving difference to the inclinations of the first andsecond light projecting optical systems as a whole in the verticaldirection. As shown in FIG. 6, the spreads of the light fluxes projectedfrom the first and second light projecting optical systems aredetermined so that both light fluxes almost overlap each other at theupper end side, while there are considerable discrepancy between the twoat the lower end side. For example, in the case of the example shown inthe figure, with respect to the vertical direction, the light fluxprojected by the first light projecting optical system starts to overlapthe optical axis 14x of the objective lens at the distance of about 1.4m and covers the focus detection area at the distance of not shorterthan about 1.8 m while the light flux projected by the second lightprojecting optical system starts to overlap the optical axis 14x of theobjective lens at the distance of about 0.8 m and covers the focusdetection area at the distance of not shorter than about 0.9 m. On theother hand, regarding the horizontal direction, as shown in FIG. 5, thelight flux projected by the first light projecting optical system startsto overlap the optical axis 14x at the distance of about 0.5 m andcovers the focus detection area at the distance of not shorter thanabout 1.8 m, while the light flux projected by the second lightprojecting optical system starts to overlap the optical axis 14x at thedistance of about 0.3 m and covers the focus detection area at thedistance of not shorter than about 0.8 m. Namely, in the above case, thetwo light fluxes projected by the first and second light projectingoptical systems perfectly overlap each other at the distance of notshorter than about 1.8 m, lighting the focus detection area, but onlythe light flux projected by the second light projecting optical system,or the light flux projected by the second light projecting opticalsystem and a part of light flux projected by the first light projectingoptical system light the focus detection area at the distance rangedfrom about 0.9 m to about 1.8 m. The distance L described above gives,as described later, the sharpest projected images of the projectivepatterns of the projective pattern films 11 and 12 and the two projectedimages overlap each other perfectly at this distance.

In case the optical axis of a projection lens is spaced by the distancem (hereinafter m is referred to as the basic line length) just above theoptical axis of an objective lens, distance range (taken along theoptical axis) capable of being lighted by the light flux projected bythe projection lens (hereinafter referred to as illuminatable distancerange) is determined by the basic line length m, a degree of spread ofthe light flux projected by the projection lens, an angle θ formed bythe projection optical axis of the light projecting optical system as awhole including the projection lens and the optical axis of theobjective lens and the distance L from the projection lens up to itspoint of focus while the spread of the light flux projected by theprojection lens can be expressed by f/φ when the diameter of a lightsource is φ and the focal distance of the projection lens is f.

FIG. 7 shows a graph indicating how the illuminatable distance rangechanges with change in the angle θ in the case of f/φ=7.2 and L=5 m. Thesolid line indicates the change in the illuminatable distance range whenm=80 mm, while the broken line when m=100 mm. As shown in this graph, asθ becomes larger, the illuminatable distance range moves to the side ofnear distance as a whole, and as m becomes smaller, the illuminatabledistance range also moves to the side of near distance as a whole. Theilluminatable distance range does not coincide with the focus detectiondistance range where focus detection is made possible since the focusdetection distance range is set within the range where the focusdetection area is covered by the light flux projected by the lightprojecting optical system. However, the focus detection distance rangemoves to the side of near distance as the movement of the illuminatabledistance range to the side of near distance and moves to the side of fardistance as the movement of the illuminatable distance range to the fardistance side. Therefore, the tendency of the change in theilluminatable distance range shown by the graph of FIG. 7 is alsoapplied to the focus detection distance range. However, it is essentialfor focus detection that an object lighted by the projected light fluxhas brightness higher than a certain level. Therefore, the practicallongest limit of the focus detection distance range is restricted by thebrightness of light source which is definite.

Meanwhile, in case the lighting device S having the first and secondlight projecting optical systems is mounted on a camera C by amechanical coupling constituted by the leg 4 and the accessory shoe 2,it is difficult to avoid occurrence of play in the mechanical coupling,which results in change in the directions of the projection optical axes7X and 8X of the first and second light projecting optical systems. Thechange in the directions of the projection optical axes leads to, forexample, deflection of the projected light fluxes indicated by an angleδ in FIG. 6 in the vertical direction (the two dotted chain line and thethree dotted chain line indicate the light fluxes projected by the firstlight projecting optical system and the second light projecting opticalsystem and deflected by the coupling play, respectively.) Suchdeflection of the light fluxes certainly gives influence on the focusdetection distance range and degree of such influence is larger in thefar distance range than in the near distance range. However, influenceby deflection of the projected light fluxes can be suppressed to becomparatively small in practice in case where the light fluxes projectedby the first and second light projecting optical systems substantiallyoverlap each other at the upper end and intersect the focus detectionarea at the longer distances (refer to FIG. 6), since the focusdetection distance range is limited by the brightness of light source inthe far distance side.

FIGS. 8A and 8B respectively show how the light fluxes projected by thefirst and second light projecting optical systems overlap each other atthe distances of 1.0 m and 5.0 m in the first embodiment describedabove, together with the focus detection area. In these figures, W₁ andW₂ represent the cross-sections of the light fluxes projected by thefirst and second projection optical systems and E represents the focusdetection area. It should be understood that the positional relationshipbetween the cross-sections W₁ and W₂ of the light fluxes and the focusdetection area E is illustrated in these figures with the side of thecross-sections of the light flux taken as a reference. Accordingly it isseen that the focus detection area E moves relative to thecross-sections W₁ and W₂ of the light fluxes within the range indicatedby the broken line due to the coupling play between the lighting deviceS and the camera C.

According to the first embodiment, the light flux projected by thesecond light projecting optical system for illumination of a neardistance area spreads in the transverse direction to the extentunnecessary for the focus detection even in case the coupling playbetween the lighting device S and the camera C is considered. That is, apart of the light flux deflected in the transverse direction from thefocus detection area E (a cross-section of such a part being indicatedby hatching in FIG. 8A) does not contribute to the illumination of thefocus detection area. FIG. 9 shows a lighting device according to asecond embodiment of the present invention which can improve thelighting efficiency by reducing such ineffective light flux.

In FIG. 9, 57 and 58 represent light source devices constituted by lightemitting diodes (not shown) and light collecting portions 57a and 58aformed as spheres of the same radius. First and second projection lenses59 and 60 have the equal focal length and projective pattern films 61and 62 are respectively provided at the focal points thereof. Atransparent protective panel 90 arranged in front of the projectionlenses 59 and 60 has a prism or optical wedge 92 at its region where apart of the light flux projected by the projection lens 60 transmits.The prism 92 is formed at the rear side of the panel 90. The width ofprism 92 is comparatively small as compared with the width of theprojected light flux in the vertical direction but is almost equal tothe width of the projected light flux in the horizontal direction. As isapparent from the figure, the prism 92 has the section of triangle andthe lower part is thicker than the upper part. The section indicated bythe hatching indicates a part of the projected light flux which haspassed through the prism 92 and this part is about 10% of the wholelight flux projected by the second light projecting optical system.

In FIG. 10 illustrating only the second light projecting optical system,pencils of light 94 and 96 passing through the outer most part (in thevertical direction) of the projection lens 60 pass the flat part ofpanel 90. Since the front and rear surfaces of the panel 90 are parallelwith each other at the area through which these pencils of light pass,the directions of the pencils of light are unchanged in front of and atthe back of the panel 90. Meanwhile, pencils of light 98 and 100 passingthe upper and lower ends of the prism 92 are deflected downward by theangle of half the vertical angle φ of the prism 92.

Referring to FIG. 11 illustrating the paths, viewed from the verticaldirection, of the light fluxes projected from the first and second lightprojecting optical systems in the second embodiment, the projectionoptical axes 57X and 58X of the first and second light projectingoptical systems cross the optical axis 14X of the objective lens at thedistance of 3 m, respectively.

FIG. 12 illustrates the light paths of the second embodiment where thefocal lengths f of the first and second projection lenses 59 and 60 areset to 22 mm, widths φ of portions 57a and 58a are set to 2.4 mm, thebasic line length m is set to 108 mm, the angle φ is set to 7°, andmoreover the optical axes 57X and 58X of the first and second lightprojecting optical systems cross the optical axis 14X of objective lensat the distance of 3.2 m respectively, viewed from the horizontaldirection. The region between pencils of light 94 and 96 indicates therange of spread of the projected light flux which does not pass theprism 92. This range covers the focus detection area E at the distanceof not shorter than about 1.2 m. Meanwhile, the region defined bypencils of lights 98 and 100 indicates the range of spread of the lightflux which has passed through the prism 92. This range covers the spreadof focus detection area E in the range from the distance of about 0.8 mto the distance of about 1.25 m. FIG. 13 is a cross-section of the lightfluxes in the second embodiment at the distance of about 2 m. The areawithin a circle 92 indicates the cross-sections W₁ and W₂ of theprojected light fluxes which have not passed through the prism 92 andthe area 94 outside the circle indicates the cross-section W₂ ' of thelight flux which has passed through the prism 92. In this secondembodiment, the degree of spread of the light fluxes through theprojection lenses 59 and 60 of the first and second light projectingoptical systems is set equal to each other and the light flux havingpassed through the second projection lens 60 is spreaded by the prism 92only in the vertical direction. Therefore, as is apparent fromcomparison of FIG. 13 and FIGS. 8a and 8B a part of light flux whichdoes not contribute to the illumination of the focus detection area Ecan be reduced as compared with the first embodiment.

In the second embodiment, difference is generated in the intensities ofthe light flux having passed through the prism 92 in accordance with theamount of separation l (refer to FIG. 10) of the prism 92 in thevertical direction from the optical axis 58x of the projection lens 58.Such difference is generated because the light emitted from the lightemitting diode included in the light source device 58 has an intensivedirectivity toward the optical axis 58x of the projection lens 58.Therefore, the light flux which is collected by the condenser portion58a and then directed to the projection lens 60 becomes more intensiveat its portion closer to the optical axis 58x of projection lens.Accordingly, as the amount of separation l is set smaller, the lightflux having passed through the prism 92 is more intensified. Namely, theintensity of the light flux can be set arbitrarily by selecting theamount of such separation as described later in detail.

FIG. 14 illustrates only a principal part of the second light projectingoptical system in a first modificating of the second embodiment. In thismodification, a prism 92' is formed as the inclined surface at atransparent panel 90' so that the panel 90' has the thicknesses t₁ andt₂ of the two stages at the upper and lower sides of the inclinedsurface. A part of the panel 90' where the light flux from the firstprojection lens not shown but corresponding to the lens 59 passes isformed as the parallel plate of thickness t₁ (or may be t₂). In therange shown in the figure, the light flux projected by the projectionlens 60 is being converged. This light flux is once converged at aposition near the panel 90' (outside the figure) and thereafter divergedto cover the focus detection area within a wider distance range.

FIG. 15 illustrates the second light projecting optical system in asecond modification of the second embodiment. Panel 90" is inclined withrespect to the projection optical axis 58x and formed with a prism 92"which has a curved surface recessed cylinrically with the radius R.Since this prism 92" has the curved surface recessed cylindrically, theprojected light flux which has passed through the prism is diverged asindicated in the figure and the intensity of the light flux becomeshigher at the upper part, while becomes lower at the lower part.Therefore, in the distance range where the light flux projected by theprojection lens 60 covers the focus detection area, the illumination orlighting becomes weaker in the nearer distance but is more inetnsifiedat the farther distance, improving the lighting efficiency.

The lighting efficiency can further be improved by forming a cylindricalprism having an aspherical cross-section in place of the prism 92". Theprism 92" does not give any adverse effect for projection of aprojective pattern consisting of vertical strips described later.

FIG. 16 illustrates a lighting device according to a third embodiment ofthe present invention. The lighting device of this embodiment isprovided with first, second and third light projecting optical systemswhile only one light source device 107 having a spherical condenserportion 107a is used in common as the light source of these lightprojecting optical systems. Since the projective film pattern 112 isused also in common for the first, second and third light projectingoptical systems, positioning of separate projective pattern films is nolonger necessary, unlike the first and second embodiments. In FIG. 16,projection lenses 109, 110 and 111 belonging to the first, second andthird light projecting optical systems respectively are stacked in thevertical direction as shown. Prisms 142 and 143 belonging to the firstand third light projecting optical systems respectively having acylindrically recessed spherical or aspherical curved surface as shownin FIG. 15. In this embodiment, the light fluxes emerging from thespherical condenser portion 107a of the light source device 107 aresplitted into first, second and third projected light fluxes and thefirst and third projected light fluxes among them are refracted by theprisms 142 and 143 in such a direction as coming close in parallel tothe projection optical axis of projection lens 110. Thereby, the first,second and third projected light fluxes respectively, as shown in FIG.17, a far distance region, intermediate distance region and neardistance region. In case the angles of the spread of the first, secondand third projected light fluxes in the vertical direction is α₁, α₂ andα₃, the lighting efficiency can be improved by setting these angles inthe relation as α₁ <α₂ <α₃ by changing the focal lengths of theprojection lenses 109, 110 and 111.

It has already been described that various problems are still unsolvedfor practical use of focus detection systems utilizing an auxiliarylight from a lighting device and that a typical problem among them isimprovement of lighting efficiency for objects within a distance rangefrom a near to far distances. Moreover, selection of a light source forproducing an auxiliary light and the wavelength of the auxiliary lightand selction of a projective pattern are also remaining as the subjectto be further discussed. A problem of a light source for producing anauxiliary light and the wavelength of the auxiliary light is describedfirst. As a light source, those which consumes less power are desirable,and currently a light emitting diode is just suitable. In case a lightemitting diode is used as the light source for focus detection,efficiency for converting electrical energy into light energy, a degreeof stimulus of lighting for human eyes and influence on chromaticabberation of an objective lens must be considered. Here, efficiency forconverting electrical energy into light energy depends on the length ofthe light emitted by light emitting diode and such energy generallybecomes higher as the wavelength becomes longer. Meanwhile, if a personis irradiated with a light having high degree of stimulus for human eyesby his face, he will close his eyes because he feels dazzling.Therefore, a picture is taken disadvantageously while he is closing hiseyes. As shown in FIG. 18 in which logarithmic values are plotted on thevertical axis, the degree of stimulus also depends on wavelength and ithas a tendency to become smaller while wavelength becomes longer withinthe range from almost the center of visible light region to the infraredregion. For example, in the case of the light having the wavelength of700 nm, the degree of stimulus becomes about 1/10 of that of the lighthaving the wavelength of 660 nm. From this point of view, it seemsdesirable to use so-called infrared light as the auxiliary light forfocus detection. However, an infrared light gives too large influence onthe chromatic aberration of an objective lens. As such influence changeslargely due to the change in focal length of the objective lens and thechange in the position of the objective lens moved for focusing, it isvery difficult to accurately correct difference in amount of chromaticaberration between the infrared light and the visible light. As aresult, it can be said that it is most desirable in total to use a lightemitting diode which emits the light of almost single wavelength ofabout 700 nm as the light source for producing auxiliary light for focusdetection.

However, there is another problem in case a light emitting diode is usedas the light source. Namely, light emitted from a light emitting diodeis similar to a monochromatic light having the spread of only about 50nm while sensitivity of light sensing elements of the image sensingdevice 24 is spreading in the range from about 380 nm to 780 nm, so thatdifference is generated in the contrast of the object sensed by theimage sensing device between the case where the object is lighted by anatural light or a fluorescent lamp and the case where it is lighted bythe light emitted from the light emitting diode. Namely, almost allsubstance tends to have a larger reflectivity as the wavelength of lightlighting the same becomes longer. In general, difference in contrastbecomes smaller than difference in colors for the light with thewavelength of about 700 nm. Therefore, upon sensing by the image sensingdevice, a substance which shows a high contrast under the illuminationby natural light often shows low contrast under the illumination by thelight emitted from the light emitting diode. FIG. 19 shows a spectralreflection factors of a green, bluegray and white objects. For the lightof wavelength near 700 nm, difference in reflectivity between green andblue gray objects is smaller than that for the light of 500 to 600 nmwhich is at the center of visible light region. When contrast of anobject is thus lowered by the illumination by an auxiliary light, thefocus detection accuracy is deteriorated in general in the T.T.L. focusdetection system (the focus detection is disabled in an extreme case),making it meaningless to use the auxiliary light. Namely, if there is nocontrast on an object it is difficult to detect the coincidence betweenthe two reimaged images even in the case of the T.T.L. focus detectionsystem of the phase difference detection type described above andtherefore this problem becomes a serious defect if it is left unsolved.

In order to solve such a problem, a light emitting diode which emits thelight of almost single wavelength of about 700 nm is used as a lightsource of the light source devices 7, 8, 57, 58 and 107 (as a such lightemitting diode, a light emitting diode of GaA As type recently developedas the light source for optical fiber communication is most desirable)and at the same time projective pattern films 11, 12, 61, 62 and 111 arearranged at the focal point of the projection lenses 9, 10, 59, 60 and109.

FIG. 20 illustrates an example of projection pattern films 11 and 12used for the above embodiments. This film is provided with a projectionpattern consisting of vertical stripes. In the figure, the hatched areasrepresent opaque parts, while the remainder represent transparent parts.When the width of an opaque part is defined as p, while the width of atransparent part is defined as q, p and q are respectively different ateach of the opaque and transparent parts and the repetition pitch (p+q)is completely irregular. The projective pattern films 11 and 12 arearranged, for example, as shown in FIG. 4 near the rear focal point ofthe projection lenses 9 and 10, respectively. The projection lenses 9and 10 project the images of the projective patterns on an object. Evenwhen the contrast on the object becomes small with the illumination bythe light from a light emitting diode of almost single wavelength asdescribed above, the images of the projective patterns provide theobject with sufficiently high contrast. The contrast thus providedsolves the problem of difficulty of focus detection by the T.T.L. focusdetection system. Since the films 11 and 12 are located near the rearfocal point of the projection lenses 9 and 10 respectively, the imagesof projective patterns become sharpest at the location in the distance Lof FIG. 4 to overlap each other perfectly.

Widths of the opaque parts of the projective pattern of the filmdescribed above are determined as explained below, considering the widthof each light sensing element of the image sensing device 24, forexample, CCD, used in the focus detection system.

FIG. 21 illustrates image of a projective pattern consisting of a singleopaque part projected on a plain object, which is viewed from the focusdetection surface together with the field frame. From the point of viewof the optical system shown in FIG. 3, FIG. 22 illustrates one of thetwo projective pattern images reimaged on the light sensing surface ofthe image sensing device positioned at the plane 30 and the focusdetection area E which is the image of the field frame 26. In thisfigure, x represents a width of each light sensing element of the imagesensing device, namely CCD, while h represents a width of the image ofthe opaque part of the projective pattern reimaged on the image sensingdevice. When x>h, the signal output of the light sensing element onwhich the image of the opaque part of the projective pattern is formednot only becomes weak but also does not change even when the image ofthe opaque part of the projective pattern moves within the area of thelight sensing element. Therefore, position of the image of the opaquepart of the projective pattern on the image sensing device cannot bedetected accurately. In contrast, when x<h, such problem is notencountered. However, it is not desirable that h is excessively largerthan x because if, so, there is a fear that the focus detection area asa whole may be occupied by the image of the opaque part of theprojective pattern. Moreover, as a practical problem, aberration of theobjective lens and brurring of the projective pattern image on the imagesensing device dependent on the focusing condition widen the width h ofthe image of the opaque part of the projective pattern and makesdifference in outputs of the adjacent two light sensing elements smallerthan it is, whereby it is difficult to carry out focus detection bydetecting coincidence between the two images reimaged on the imagesensing device. As a consequence, a comparatively desirable result canbe obtained by setting a value of h to the range of about 3h≧x≧h/2 underthe focused condition where the projective pattern image is focused onthe image sensing device and by always forming a plurality of images ofopaque parts as the projective pattern image within the focus detectionarea. However, the width h of the image of the opaque part of theprojective pattern on the focus detection surface differs depending onthe angle of field of the objective lens, for example, a kind ofinterchangeable lens attached to the camera. Namely, it becomes narrowerfor a wide angle lens as compared with a standard lens but becomes widerfor a telephoto lens. Accordingly it is desirable to take it intoconsideration that the angles of fields of all interchangeable lenses tobe used satisfy the above condition. Meanwhile, when a plurality ofopaque parts of an equal width are provided on the projective pattern,the two projective pattern images formed by the reimaging lenses 21 and22 coincide with each other at a plurality of positions in the case ofthe focus detection system of the phase difference type shown in FIG. 3,resulting in failure of correct focus detection. In the case of a wideangle lens, the focus detection area becomes comparatively wide.Therefore, when the same arrangement of some opaque and transparentparts is repeated in the projection pattern, the same images of theopaque and transparent parts are repeatedly formed within the focusdetection area, also resulting in failure of correct focus detection.For these reasons, the film of FIG. 20 has the projective pattern inwhich not only the width p of opaque parts but also the repetition pitch(p+q) of the opaque and transparent parts are perfectly irregular. Thearrangement and the width of the opaque and transparent parts of theprojective pattern are determined as described above. However, in casethe lighting device S is coupled with the camera C by means of amechanical coupling means like the embodiments described above, it isdesirable to increase the number of the opaque parts, considering amargin of deflection angle δ due to the coupling play, as compared withthe case where the lighting device S is fixedly provided on the cameraC.

In the projection pattern of the projection pattern film shown in FIG.20, the opaque parts having a narrower width are arranged at acomparatively narrow interval while the opaque parts have a wider widthare arranged at a comparatively wider interval. This makes it possibleto detect the coincidence between the two images formed by the reimaginglenses 21 and 22, based on the projected images of the narrower opaqueparts in case the focus detection area becomes relatively narrow by useof a telephoto lens, and based on the projected images of the wideropaque parts in case the focus detection area becomes relatively widerby use of a wide angle lens. Accordingly, influence on focus detectioncapability resulting from difference in the angale of field of aninterchangeable lens can be reduced as much as possible.

FIG. 22 illustrates a modification of the projective pattern film shownin FIG. 20. Also in this modification, the widths p and q of the opaqueparts and the transparent parts of the projective pattern arerespectively different and the pitch (p+q) is irregular.

The opaque parts at opposite lateral ends of the two projective patternfilms described above are formed with protruded portions a₁, a₂ and a₃.The protrusion a₁ is located at the intermediate position between theprotrusions a₂ and a ₃ in the vertical direction. The projective patterncan be positioned in the first and second projection optical systems byobservation of projected images of these protrusions.

FIG. 23 illustrates the range of overlapping of the projected patternimages in the case where the projective pattern films are arranged inthe first and second light projecting optical systems as shown in FIG.4. For brevity of explanation, it is assumed that only one opaque partof width p is provided as shown in FIG. 24 in the respective projectivepatterns at the area spaced to the outside by the distance a from theoptical axis of the respective projection lenses in the horizontaldirection. Moreover, it is also assumed that the focal length and thediameter of the respective projection lenses are f and b, respectively.The distance between the optical axes of the two projection lenses is Dand the distance to a position where the projected images of twopatterns perfectly coincide with each other is L. Here, in order todetermine the degree of overlapping of the images of the two projectedpatterns at the areas in front of and at the back of the position of thedistance L, the distances L_(MIN) and L_(MAX) to the positions where theoverlapping area becoms 1/2 in the respective projected images areobtained below. In this case, the coordinate x is plotted forward inparallel to the optical axes of the projection lenses 9 and 10 from thepositions of these projection lenses, while the coordinate y is plottedin the direction crossing the coordinate x at the right angle on thehorizontal surface from the optical axis of one of the projectionlenses. ##EQU1##

Wherein, b<<L, and Y_(max) and Y_(min) respectively indicate theoutermost pencils of light of the light flux having passed through oneof the projection lenses for projection of the image of thecorresponding projective pattern. On the other hand, the center pencilof light of this light flux is expressed by ##EQU2##

In this case, the conditions where the twolight fluxes for projection ofthe images of the projective patterns overlap each other in half or morecan be expressed as indicated below:

    when x≧L, y+y.sub.min ≧D                     (6)

    when x<L, y+y.sub.max ≧D                            (7)

From the equations (2), (3), (5), (6) and (7), the following relationscan be obtained. ##EQU3##

For example, when L=3 m, f=18 mm, p=0.1 mm, b=8 mm and D=20 mm, L_(MAX)=5.1 m and L_(MIN) =1.7 m are obtained from the equations (8) and (9)and L_(MAX) =6.4 m and L_(MIN) =1.4 m can be obtained only by changing Dto 15 mm. Also, L_(MAX) =6.0 m and L_(MIN) =1.6 m can be obtained onlyby changing p to 0.12 mm. From these facts, overlapping of the twoprojected pattern images can be kept at 1/2 or more in wider range ifthe distance D between the two projection lenses is set to a small valueor the width p of the opaque part of the respective projection patternsis set to a large value.

When the degree of overlapping of the two projected pattern images isreduced, contrast of the projected pattern images on an object islowered correspondingly and it becomes difficult to detect coincidencebetween the two images of the object formed on the image sensing deviceby the reimaging lenses. The overlapping of the two projected patternimages at 1/2 or more area is a practical condition for allowing thedetection of the coincidence between the two images of the object andthis condition is more severe in the near distance side than in the fardistance side (the distance range starting from the point of distance Lbecomes narrower in the near distance side than in the far distanceside). However, the projected light flux is intensive in the neardistance side, so that even in case the degree of the overlapping of thetwo projected pattern images is smaller than 1/2, the contrast of theprojected pattern images on an object tends to be kept comparativelyhigh in the near distance side. Therefore focus detection is actuallymade possible even in distances nearer than the L_(MIN) obtained by theequation (9 ).

FIGS. 25A and 25B illustrate composite type projection lenses which havereduced distance D. It should be recalled that the degree of theoverlapping of the two projected pattern images can be kept at thepredetermined value or more by setting the distance D to a small value.The two projection lenses 159 and 160 are integrally formed on a singletransparent plate 150 made of a synthetic resin to be in contact witheach other at the boundary 162. When the radius of the respective lenses159 and 160 is r, the distance D between the lenses is set as D<2r.

The first to third embodiments of the present invention and somemodifications thereof have been described but still furthermodifications to the embodiments can be thought of. For example, thelighting device S may be providedon an accessory independently of anelectronic flash device. The lighting device S can be mounted not onlyon the accessory shoe of the camera but also on any desired part of thecamera when the camera is provided with a suitable coupling member.Moreover, the lighting device S can be fixedly provided on the camerabody. In this case, it is desirable that the lighting device is providedjust above, just below or just aside the objective lens of the camerabecause the focus detection area is extending while generally spreadingin the lateral direction and vertical direction, but this is notessential to the present invention.

Next, explanation is given of embodiments of the present invention whichhave improved light source devices.

Referring to FIG. 26 showing first and second light projecting opticalsystems of a lighting device according to a fourth embodiment of thepresent invention, 209 and 210 denote projection lenses of the sameshape. The lenses 209 and 210 are disposed so that the respectiveoptical axes 209X and 210X are parallel to each other and spaced by adistance D. 207 and 208 denote light source devices which are disposedbehind the projection lenses 209 and 210 respectively so that opticalaxes 207X and 208X thereof intersect each other at a position spaced bya distance L from the projection lenses 209 and 210. More specifically,the light source devices 207 and 208 are provided at their front faceswith spherical light condensing molded portions 207a and 208a. Thecenters of the spherical surfaces of the portions 207a and 208a arespaced by a distance d in directions opposite to each other from theoptical axes 209X and 210X of the projection lenses. When radii ofcurvature of the spherical surfaces of the molded portions 207a and 208aare r₁ and r₂ , respectively, r₂ is larger than r₁. In the verticaldirection in the figure, the centers of both spherical faces aredeviated from each other by the difference Δ(=r₂ -r₁) between the radiiof curvature so that lower ends of both spherical surfaces coincide witheach other. Thus, the illumination area W₂ illuminated by the light fluxfrom the light source device 208 and the illumination area W₁illuminated by the light flux from the light source device 207 arealways coincident with each other at their upper ends and theillumination area W₁ is included in the illumination area W₂, as shownin the figure.

FIG. 27 is a schematic view showing a positional relationship betweenthe light fluxes and the focus detecting area E. In this figure, φNrepresents the light flux emitted from the light source device 208provided with the molded portion 208a having the spherical surface ofradius r₂, and φF represents the light flux emitted from the lightsource device 207 provided with the molded portion 207a having thespherical surface of radius r₁. As previously noted, since bothspherical surfaces are coincident with each other at their lower ends,the light fluxes φN and φF are rendered coincident with each other attheir upper ends. And since r₂ is larger than r₁, then spread of thelight flux φN is larger than that of the light flux φF. Therefore, thelower ends of both light fluxes φN and φF deviate from each other.

The light flux φN illuminates a distance zone within the focus detectionarea E farther than lN, while the light flux lF illuminates a distancezone within the focus detection area E farther than lF which is longerthan lN. Therefore, the distance zone within the focus detecting area Earther than lF is illuminated by both light fluxes φN and φF, while thedistance zone within the focus detecting area E from lN to lF isilluminated only by the light flux φN. Accordingly, an object locatedwithin the focus detection area at a relatively far position isilluminated by a light corresponding to the overlapping light fluxes φNAND φF, while an object located within the focus detection area at arelatively close distance (from lN to lF) is illuminated by a lightcorresponding to the light flux φN alone. Therefore, no matter in whichposition from short to long distance the object may be located, it canbe illuminated by light having a sufficiently high intensity, thuspermitting accurate focus detection.

Referring to FIG. 28 showing the construction of the light sourcedevices 207 and 208, 228 denotes a unit member molded of a colorlesstransparent epoxy resin or the like. The unit member 228 is provided atits front with the light condensing portion 207a(208a). The radius ofcurvature of this spherical surface is assumed to be R (r₁, r₂). 230denotes a first frame fixed to the unit member 228. At the front face ofthe first frame 230 is formed a conical recess 232 and on the innersurface of the recess 232 is vapor-deposited a material of a highreflectance such as gold or silver to enhance the reflectivity. With thefirst frame 230 fixed to the unit member 228, the recess 232 is locatedin a position of rotational symmetry relative to the optical axis of thespherical light condensing portion 207a (208a). Furthr, the recess 232is in the form of a cone which diverges forward from the bottom. If theradius of the bottom is φb and that of the inlet is φa, φa is largerthan φb.

To the bottom of the recess 232 is fixed a light emitting diode 234 soas to be positioned on the optical axis of the spherical lightcondensing portion 207a(208a). The light emitting diode 234 emits lightfrom its front face 234a and side faces 234b. It is sticked to thebottom of the recess 232 with paste or the like and is electricallyconnected to the first frame 230. 236 denotes a second frame which isbonded to the unit member 228 and is electrically connected to the lightemitting diode 234. The distance from the vertex of the portion207a(208a) to the light emitting diode 234 is here assumed to be h asshown.

In such construction, not only the light (hereinafter referred to as"front-face light") emitted from the front face 234a of the lightemitting diode 234 but also the light (herein after referred to as"side-face light") emitted from the side faces 234b of the same diode isprojected forward thereby permitting an efficient illumination for anobject within the focus detection area. Assuming that the size of thelight emitting diode 234 and the quantities of the lights emittedtherefrom are unchanged, the quantity of light projected toward anobject varies depending on F number FNO of the projection lens, radiusof curvature R of the portion 207a(208a), distance h from the portion207a(208a) to the light emitting diode 234, angle of the slope of therecess 232 and the depth of the same recess. Therefore, these conditionswill be considered below.

FIG. 27 shows a light flux which is emitted from the front face 234a ofthe light emitting diode 234 to be projected on an object. It is hereassumed that R is 1.2 mm, h is 2.3 mm and the width k of the front face234a of the light emitting diode 234 is 0.3 mm. l represents thedistance from the front face 234a to the center of curvature of thespherical surface of the portion 207a(208a). l=h-R. F number FNO of theprojection lens is assumed to be 1.2. Since the angle of the lightincident on the spherical surface of the porton 207a(208a) and that ofthe light emanating from the spherical surface vary according to l, thelight beam projected on the focus detecting object through theprojection lens varies according to l. This is shown in the graph ofFIG. 30.

In the graph of FIG. 30 showing relationship between change in the totalquantity of light projected from the projection lens and change in l/R,a curve ○1 reflects the case of the projection lens of FNO=1.2 and acurve ○2 reflects the case of the projection lens of FNO=2.0. The curve○1 indicates that, in the case of the projection lens of FNO=1.2,sufficient illumination is provided by the light emanating from thefront surface 234a of the light emitting diode 234 if l/R is within therange of 0.6 to 1.1, preferably 0.8 to 0.9. On the other hand, the curve○2 indicates that, in the case of the projection lens of FNO=2.0,sufficient illumination is provided by the light emanating fron thefront face 234a of the light emitting diode 234 if l/R is within therange of 0.8 to 1.3, preferably 1.0 or thereabouts. Thus, once FNO isgiven, an l/R value providing good illumination efficiency isdetermined, and l can be determined once R is determined according tothe width of the projected light flux (φN, φF in FIG. 27).

FIGS. 31 to 35 show how the light flux emitted from the side faces 234bof the light emitting diode 234 to be projected on an object changeswith change in the angle of the inclination of the recess 232. In thesefigures there are shown light fluxes in the three cases of the distanceh being 2.2 mm, 1.9 mm and 1.6 mm (i.e. l=1.2 mm, 0.9 mm and 0.6 mm) andthe radius of curvature R of the spherical surface of the lens portion207a (208a) being 1 mm. In these figures, moreover, the two dotted chainlines represent pencils of light in the case of h=2.2 mm, the one dottedchain lines represent pencils of light in the case of h=1.9 mm and thedotted lines represent pencils of light in the case of h=1.6 mm. FIG. 31shows the case where the angle α of the inclination of the recess 232 is30°, φa=1.94 mm, φb=0.83 mm, K=0.35 mm, the depth of the recess is 0.32mm, the distance t from the upper face 234a of the light emitting diode234 to the side-face light emitting position is 0.05 mm, and F_(NO) ofthe projection lens is 1.2.

In FIG. 32 α=35° and φa=1.74 mm; in FIG. 33 α=44° and φa=1.5 mm; in FIG.34 α=55° and φa=1.28 mm; and in FIG. 35 α=65° and φa=1.13 mm. In all ofFIGS. 32 to 35 the depth of the recess is 0.32 mm. If h=1.6 mm (l=0.6mm) in FIG. 34 wherein α=55°, there is no side-facelight projectedtowards an object through the projection lens, and in the two cases ofh=1.6 mm (l=0.6 mm) and h=1.9 mm (l=0.9 mm) in FIG. 35 wherein α=65°,there is no side-face light projected towards an object through theprojection lens. Thus, in these cases the light emitted from the sideface of the light emitting diode 234 cannot be used at all for lightingan object within the focus detection area, that is, the lightingefficiency is poor.

The relationship between change in the angle α of the inclination of therecess 232 an change in the quantity of light emitted from the sidefaces of the light emitting diode 234 for illumination of an object issummarized graphically in FIG. 36. FIG. 36 shows how the quantity oflight emitted from the side faces (the position of t=0.05 mm) of thelight emitting diode 234 to be used for illumination through theprojection lens changes with change in the angle α, in terms ofcalculated values with respect to the cases of h=2.2 mm (l=1.2 mm)(curve ○1 ), h=1.9 mm (l=0.9 mm) (curve ○2 ) and h=1.6 mm (l=0.6 mm)(curve ○ ), assuming R=1.0 mm and FNO=1.2. In the case of the projectionlens of FNO=1.2, it is when l/R is within the range of 0.8 to 0.9 asshown in FIG. 30 that the light emitted from the front face 234a of thelight emitting diode 234 can be used for illumination efficiently. Inaddition, it is seen that in the case of l=0.9 mm, the lightingefficiency of the side-face light is high when α is in the range of 40°to 45°. Thus, in the case of the projection lens of FNO=1.2, l/R and αshould be in the ranges of 0.8 to 0.9 and 40° to 45° respectively inorder that both front and side-face light fluxes can illuminate anobject within the focus detection area efficiently.

FIG. 37 shows how the quantity of light emitted from the side faces (theposition of t=0.05 mm) of the light emitting diode 234 changes withchange in the angle α, in terms of calculated values with respect to thecases of h=2.2 mm (l=1.2 mm) (curve ○1 ), h=1.9 mm (l=0.9 mm) (curve ○2) and h=1.6 mm (l=0.6 mm) (curve ○3 ), assuming R=1.0 mm and FNO=1.7.From FIG. 37 it is seen that in the case of the projection lens ofFNO=1.7, the lighting using the side-face light is most efficient at avalue of α=35° or thereabouts. FIGS. 36 and 37 are drawn on the samescale. From these figures, it is seen that with increase of FNO, thedecrease in quantity of the side-face light is large as compared withthat of the front-face light. It is also seen from these figures thatwith decrease of h (i.e. l), the angle α of the recess 232 providing themost efficient lighting by the sideface light becomes smaller.

FIG. 38 is a graph showing the results of actual measurement of changein the light quantity of all light fluxes projected from the projectionlens to be used for illumination, due to changes in the distance h, inthe case of R=1.2 mm, FNO=1.2 and α=45°. From FIG. 38 it is seen thatthe maximum light quantity for illumination is obtained in the vicinityof h=2.2-2.3 (i.e. l=1.2-1.3 mm). Since R=1.2 mm, l/R becomes 0.8 to 0.9and this well concides with the foregoing conclusion based oncalcualtion. That is, it is seen from FIG. 38 that the value of h forobtaining a good lighting efficiency is in the range of 1.9 to 2.5 mm,and also actually it has thus been confirmed that the range of l/R=0.6to 1.1 is desirable for R=1.2 mm in the case of the projection lens ofFNO=1.2.

FIGS. 39A and 39B illustrate change in the width of the side-face lightflux incident on the projection lens (FNO=1.2) due to change in theradius of curvature R of the spherical surface in the case of α(=45°).In FIG. 39A R=0.8 mm and in FIG. 39B R=1.0 mm but l/R is kept unchangedin FIGS. 39A and 39B. The front-face light flux does not change withchange in R. From a comparison between FIGS. 39A and 39B it is seen thatas R becomes smaller, the side-face light flux incident on theprojection lens becomes narrower and its quantity decreases. That is, asR is made smaller while maintaining l/R constant, the quantity ofillumination light based on the side-face light flux decreasesgradually. However, where the focal length of the projection lens iskept unchanged, the smaller the R, the smaller becomes the width of thelight flux (corresponding to the foregoing φN or φF) projected toward anobject within the focus detection area, and therefore the luminosityover the object rather increases.

FIG. 40 shows change in luminosity over an object within the focusdetection area relative to change in R (unit: mm) under the conditionsof FNO=1.2 and α=45° and at l/R=0.9 (h=0.9R). From FIG. 40 it is seenthat the relative lumimosity over the object increases with decrease ofR, but when R becomes smaller than 1.0 mm, the increase of the relativeluminosity is discontinued due to decrease of the side-face light fluxitself. Therefore, in order to use the side-face light flux efficientlyfor illumination, a value of R of 1.0 mm or thereabouts is mostdesirable. In the embodiment illustrated in FIG. 26, therefore, the l/Rvalue is made common between the two light source devices 207 and 208and the radius of curvature r₁ of the spherical surface of the moldedportion 207a of the light source device 207 is made smaller than theradius of curvature r₂ of the spherical surface of the molded portion208a of the light source device 208 while r₁ is set near 1.0 mm.Therefore, since r₂ is larger than r₁, r₂ is larger than 1.0 mm. In sucha construction, the luminosity over an object based on the light flux φFis higher than that based on the light flux φN. This makes it possibleto give a higher luminosity to an object lying at a long distance sidewithin the focus detection area than to an object lying at a shortdistance side within the focus detection area.

FIGS. 41 to 49 relate to further embodiments of the present invention towhich a projective pattern is formed integrally with a sphericaltransparent molded portion of a light source device.

Referring to FIG. 41 showing first and second light projecting opticalsystems of a lighting device according to a fifth embodiment of thepresent invention, 209 and 210 represent projection lenses of the sameshape, which are disposed in the same manner as in FIG. 26. 257 and 258designate light source devices disposed behind the projection lenses 209and 210 so that their optical axes 257X and 258X intersect each other ata position spaced by a distance L from the projection lenses 209 and210. More specifically, the light source devices 257 and 258 areprovided at their front faces with transparent molded portions 257a and258a each having a spherical surface. The centers of the sphericalsurfaces are spaced by a distance d in directions opposite to each otherrelative to the optical axes 209X and 210X of the projection lenses 209and 210. The radii of curvature of the spherical surfaces of the moldportions 257a and 258a are r₁ and r₂, respectively, and r₂ is largerthan r₁. In the vertical direction in the figure (directionperpendicular to the projection lens optical axes 209X and 210X thecenters of both spherical surfaces are deviated from each other by thedifference Δ(=r₂ -r₁) of the radii of curvature so that lower ends ofboth spherical surfaces coincide with each other. Thus, theconfigurations of the portions 257a and 258a so far explained are thesame as those of the portions 207a and 208a of the fourth embodimentshown in FIG. 26. As shown in FIG. 41, at the front faces of theportions 257a and 258a are formed a pair of very small convex portions263 and 265 and a pair of like convex portions 259 and 261 respectively.The convex portions 263 and 265 are symmetrical with respect to avertical plane including the optical axis 209X while the convex portions259 and 261 are symmetrical with respect to a vertical plane includingthe optical axis 210X.

FIG. 42 shows the construction of the light source devices 257 and 258more specifically. In this figure, 294 indicates a light source devicecorresponding to 257 and 258, and 269 denotes a unit member molded of acolorless transparent epoxy resin or the like. At the front portion ofthe unit member 296 is formed a light condensing portion 286a which hasa spherical surface corresponding to the molded portions 257a and 258a.On this spherical surface are integrally formed a pair of contrastpattern projecting convex portions 290 and 298 which are symmetricalwith respect to a vertical plane including the optical axis of the lightsource device. The convex portions 290 and 298 correspond to the convexportions 263 and 265 and the convex oprtions 259 and 261 shown in FIG.41. In the interior of the unit member 296 is fixed a frame (not shown),whose front face is formed with a conical recess 232. On the innersurface of the recess 232 is vapor-deposited a material of a highreflectance such as a gold or silver to enhance the reflectively withthis frame fixed to the unit member 296, the recess 232 is located in aposition of rotational symmetry relative to the optical axis 286x of thelight condensing portion 286a. Further, the recess 232 is in the form ofa cone which diverges forward from the bottom.

To the bottom of the recess 232 is fixed a light emitting diode 234 soas to be positioned on the optical axis 286x of the light condensingportion 286a. The light emitting diode 234 emits light from its frontface 234a and side faces 234b and it is sticked to the bottom of therecess 232 with paste or the like.

Referring to FIG. 43, on the surface of the portion 286a facing theprojection lens 209 (210) are formed convex portions 288 and 290 of ashape as shown. The convex portions 288 and 290 are symmetrical witheach other relative to a plane perpendicular to the paper surface andinclusive of the optical axis 286x and are in elongated shape in adirection perpendicular to the paper surface. Further, the direction ofthe width of the convex portions 288 and 290 (transverse direction inthe figure) is coincident with the extending direction of the lightsensing elements of the image sensing device 24 disposed within thefocus detecting device F of the camera. The convex portions 288 and 290are composed of planar light transmitting portions 288a and 290a andinclined total reflection portions 288b, 288c, 290b and 290c. From thefront surface and the side faces of the light emitting diode 234 areemitted fluxes of light of a wave length determined by the material ofthe light emitting diode.

D₁ represents a typical pencil of light radiated from one point of theoptical axis 286X at the front surface of the light emitting diode 234.If the angle of the pencil of light D₁ relative to the optical axis 286Xis β₁ and the angle of incidence of the pencil of light D₁ relative tothe total reflection portion 290b is θ, the angle α of the totalreflection portion 290b from a line P perpendicular to the optical axis286X is represented as follows:

    α=θ+β.sub.1

The condition for total reflection of the pencil of light D₁ at thetotal reflection portion 290b is as follows provided the sizes ofvarious portions are as shown in FIG. 43 and a refractive index N' ofthe transparent resin forming the portion 286a is 1.5:

    θ≧42°

On the other hand, D₂ represents a pencil of light which is emitted froman end of the front face of the light emitting diode 234 and is incidenton the lower end of the total reflection portion 288b of the convexportion 288. The pencil of light D₂ forms an angle β₂ relative to anaxis parallel to the optical axis 286A. Among the lights emanating fromthe front surface of the light emitting diode 234, the pencil of lightD₂ is incident on the total reflection portion 288b at the smallestangle of incidence. D₃ represents a pencil of light which is radiatedfrom a side face of the light emitting diode 234, and reflected at theside surface of the recess 232 to impinge on the lower end of the totalreflection portion 288b of the convex portion 288. This pencil of lightD₃ forms an angle β₂ relative to an axis parallel to the optical axis286X. In this case, among the lights emanating from the side face of thelight emitting diode 234 and reflected at the side surface of the recess232. the pencil of light D₃ is incident on the total reflection portion288b at the smallest angle of incidence. As is apparent from the figure,there exists the following relationship.

    β.sub.3 >β.sub.2 >β.sub.1

Accordingly, if the angle of the total reflection portions 288b and 290bis set to a value causing total reflection of the pencil of light D₃,there will occur total reflection of all the other pencils of lightmentioned above, so that no light emantes from the total reflectionportion. Thus, this portion observed through the projection lens appearsas a dark line, that is, a contrast pattern is projected towards thefocus detection area.

As an example, the condition for the total reflection is calculated asfollows:

    β.sub.3 =23.5°

    and α≧42°+23.5°=65.5°

Here it is assumed that the width of the chip of the light emittingdiode 234 in a direction perpendicular to the optical axis 286X is 400μm, the distance from the optical axis 286X to the reflective portion ofthe recess 232 is 500 μm, the distance from the front surface of thelight emitting diode 234 to the vertex of the portion 286a is 1.9 mm,the radius of curvature R of the spherical surface of the portion 286ais 1 mm, and dimensions of the convex portions 288 and 290 are as shownin FIG. 6.

FIG. 44 shows a projective pattern image formed by the light sourcedevice of FIG. 43. 300 represents an extent of the entire projectedimage, in which dark lines 302 and 304 are formed at portionscorresponding to the total reflection portions 288b, 288c, 290b and 290cof the convex portions 288 and 290 formed on the front face of theportion 286a. Bright portions 306 corresponding to the lighttransmitting portions 288a and 290a are located between those darkportions 302 and 304.

FIG. 45 shows a first modification of the light source device of FIG.43, which includes a large number of convex portions for increasing thenumber of dark lines. In this modification, four convex portions 358,360, 362 and 364 are formed symmetrically with respect to a planeperpendicular to the paper surface and inclusive of the optical axis286X. The convex portions 358 and 362 are formed with total reflectionportions 385b and 362b respectively so that the total reflection portion362b is closer to parallelism to the optical axis 286X. This is based onthe foregoing condition for total reflection. On the other hand, theangle (corresponding to α) and height (indicated at h in the figure) ofthe total reflection portions determine the width of dark lines of theprojected image and so may be designed as necessary. Dimensions ofvarious portions in this modification are as shown in the figure.

FIGS. 46 and 47 show a second modification of the light source device ofFIG. 43. In this figure, 366 to 378 represent a plurality of convexportions which are formed in a semicircular section along the surface ofthe portion 286a. Total reflection occurs in the vicinity of the portionwhere each such semicircle intersects the surface of the portion 286a.

FIGS. 48 and 49 show a third modification of the light source device ofFIG. 43, in which the angle α of each of projections 280 to 396 is setat 90°, so that a number of fine dark lines are formed on the projectionpattern image. The fore end face (light emitting portion) of each of theprojections 380 to 396 is in contact with a circle of radius R₂ which islarger than the radius of curvature R₁ of the portion 286a. In thiscase, the width of each projection in a direction perpendicular to theoptical axis 286X is preferably in the range of 0.1 to 0.2 mm. Such avery small projection can be easily obtained by forming its mold underthe technique of electrical discharge machining.

Although in the fifth embodiment and the first to third modificationsthereof, the spherical light condensing portion 286a is integrallyformed with the projections or convex portions for the projection of acontrast projective pattern image, recesses or concave portions may beformed in the portion 286a instead of the projections or convexportions. Further, the contrast projective pattern image to be projectedon the focus detection area may be determined according tocharacteristics of the focus detecting device and is not necessarilylimited to those of the fifth embodiment and the first to thirdmodifications thereof, constituted by bright and dark stripes.

Shown in FIGS. 52 to 67 are still further embodiments of the presentinvention in which a single light projecting optical system is used forlighting a comparatively wide distance range within the focus detectionarea. In advance to explanation of these embodiments, explanation isgiven of FIGS. 50A, 50B and 50C and 51. In FIG. 51, a light projectingoptical system is provided just above the optical axis 14X of theobjective lens although it is not shown, and B represents a separationof a light source included in the light projecting optical system fromthe optical axis 14X. The projection optical axis 408X of the lightprojecting optical system intersects the optical axis 14X of theobjective lens at a distance L from the focus detection surface of thefocus detection device F of the camera. R_(u) and R_(l) respectivelyrepresent the uppermost and lowermost pencils of light of the light fluxprojected by the light projecting optical system and L_(MAX) and L_(MIN)respectively represent the longest and shortest distance where the fluxof light projected by the light projecting optical system can cover thefocus detection area E. Thus, the focus detection area within thedistance range l_(r) from L_(MAX) to L_(MIN) is illuminated by the lightflux projected by the light projecting optical system. If the light fluxprojected by the light projecting optical system is sufficientlyintensive at any part of the focus detection area within the distancerange l_(r), focus detection is made possible with respect to all partsof the focus detection area within the distance range l_(r). FIGS. 50A,50B and 50C schematically illustrate overlapping conditions of the lightflux projected by the light projecting optical system and the focusdetection area at the distances L_(MIN), L and L_(MAX), respectively. Asis apparent from these figures, the focus detection area E overlaps anupper portion of the light flux at the distance L_(MAX) whileoverlapping a lower portion of the light flux at the distance L_(MIN).The overlapping portion moves upward and downward and the change in thedistance but does not move at all in the transverse direction even withthe change in the distance. This indicates that, in order to widen thefocus detection distance range, that is, the above described distancerange l_(r), it is necessary to widen the spread of the light flux inthe vertical direction. Further, in widening the flux in the verticaldirection, it is desirable to provide the widened flux with arectangular cross-section being longer in the vertical direction than inthe horizontal direction.

For example, in the case of B=108 mm, L_(MIN) =0.6 m and L_(MAX) =7 m,the spread of the light flux must be ±4° in the vertical direction and±1.5° in the horizontal direction if the spread of the focus detectionarea is ±0.2° in the vertical direction and ±1.3° in the horizontaldirection.

On the other hand, the intensity of light emitted from a light sourcedecreases in proportion to square of the distance from the light source.This indicates that the overlapping of the light flux with the focusdetection area at the distance L_(MAX) cannot ensure accurate focusdetection if the light flux is not sufficiently intensive within thefocus detection area at the distance L_(MAX). This will be of no problemif the light source has a large power. However, in the case a lightsource for lighting the focus detection area to help focus detection isincorporated in an electronic flash device which consumes much electricenergy of a battery upon each flashing for flash photography, it cannotbe allowed for the light source to consume so much electric energy ofthe battery. In view of such a restriction of consumption of electricenergy, it is most desirable to provide the light flux projected by thelight projecting optical system with intensity distribution as indicatedby a curve I in FIG. 50c, so that, at the distance L_(MAX), theprojected light flux has the highest intensity within the focusdetection area.

In summary, it can be understood that the most efficient illumination ofthe focus detection area is provided by a light flux which has spread ofa rectangular shape being longer in the vertical direction than in thehorizontal direction and which has such intensity distribution that anupper portion thereof becomes most intensive.

FIG. 52 shows a light projection optical system according to a sixthembodiment of the present invention.

In FIG. 52, a projection lens 409 is arranged in front of a light sourcedevice 408 and a protection transparent panel 410 integrally formed witha prism 411 at a part thereof is arranged in front of the projectionlens 409. The light source 408 desirably has a structure in which alight emitting diode emitting a visible light of a long wavelength (forexample, about 700 nm) is embedded in a unit member which is molded of atransparent resin and integrally formed with a spherical lightcondensing portion 408a at a region opposing to the projection lens 409.The position of the projection lens 409 in the direction of optical axisis determined so as to focus the spherical light condensing portion408a, for example, at the distance of 5 m. The position indicated byvirtual line 412 is the conjugate position corresponding to the distanceof 5 m. The light flux emitted from the light source device 408 iscondensed by the portion 408a to be refracted by the projection lens 409and then projected towards the object side through the parallel platepart of the protection panel 410. The range defined by the pencils oflight e_(u) and e_(l) indicates the range of spread of the light flux inthe vertical direction. A part of the light flux incident on the prism411 after having passed through the projectin lens 409 is deflecteddownward by the effect of the prism and then projected toward the objectside within the range of spread defined by the pencils of light f_(u)and f_(l). Since light intensity within the range of spread f_(u) ˜f_(l)is determined by the area of the prism 411, appropriate setting of thearea of the prism makes it possible to make the light flux having beendeflected by the prism weaker than the light flux having passed throughthe parallel plate part of the protection panel 410.

FIG. 53 illustrates the path of the light flux projected by the lightprojecting optical system of FIG. 52. The pencils of light e_(u), e_(l),f_(u) and f_(l) correspond to those in FIG. 52, respectively. The pencilof light f_(l) which has passed through the prism 411 to be deflectedthereby and the pencil of light e_(u) which has passed through theparallel plate part of the panel 410 cross each other at the distance of1 m and then partially overlaps each ther at distances longer than 1 m.

FIG. 54 is a sectional view of light flux shown in FIG. 53 at thedistance of 1 m. W indicates a light image by the light flux havingpassed through the parallel plate part of protection panel 410 and Windicates a light image by the light flux having being refracted by theprism 411. The center of the light image of the spherical portion 408adeflected by the prism 411 is formed at a position being lower by V thanthe light image W but only the crescent moon type region (the regionindicated by the width v) is projected for the reason described below asshown in the figure.

Therefore, because of the use of prism 411 as light deflecting means,the illumination light has a spread where the light image W formed bythe light flux emitted from the entire part of spherical portion 408aand having passed through the parallel plate part of the protectionpanel 410 and the light image W' formed by the light flux emitted from apart of the spherical portion 408a and deflected by the prism 411 arepartially overlapped with each other. Thus the spread of theillumination light is longer in the vertical direction than in thehorizontal direction and the intensity distribution of the illuminationlight is such that the upper side of the illumination light whichcontributes to the lighting for far distance side is more intensive thanthe lower side of the illumination light which contributes to thelighting for near distance side.

FIG. 55 is an optical path diagram for explaining the above phenomenon.The light emitted from a light eimitting diode 415 is refracted by aspherical light condensing portion 416 toward a projection lens 417.Here, as shown in FIG. 56, a panel 418 is formed with a prism 419 havingthe lateral width h_(X) and the vertical width h_(y) at the distance ofH_(Y) from the optical axis of the lens 417. Regarding the lightsemitted from a point of the light emitting diode 415 on the opticalaxis, the pencil of light a_(H) passes through the highest part of thespherical surface of the portion 416 among the lights passing throughthe prism 419, while the pencil of light a_(L) passes through the lowestpart of the spherical surface among the lights passing through the prism419. Regarding the lights emitted from a point of the light emittingdiode 415 spaced from the optical axis by the distance Y, the pencils oflight b_(H) passes the highest part of spherical surface of the portion416 among the lights passing through the prism 419, while the pencil oflight b_(L) passes through the lowest part of the spherical surfaceamong the lights passing through the prism 419. As the size of the lightemitting diode 415 is sufficiently smaller than the diameter of theportion 416 (the size of the chip of the diode 415 is actually about 0.5mm in diameter at most) and the light emitting diode 415 is locatedrather near to the center of the spherical surface of the portion 415(this location is determined in order for the projection lens 417 toreceive the maximum amount of light), the lights passing through theprism 419 are limited only to those lights which have passed through apart (almost upper half in the figure) of the portion 416. Like thepencil of light c, most of the lights having passed through the lowerside of the portion 416 do not enter the prism 419. Therefore, a lightimage of the pattern 416 projected by the projection lens 417 throughthe prism 419 is in such a shape as indicated by W' in FIG. 54.

FIG. 56 illustrates a positional relationship between the projectionlens 417 and the prism 419 viewed from the front. As shown the lateralwidth h_(X) of the prism 419 is sufficiently longer than the verticalwidth h_(y), so that an image of every part of the portion 416 of thewidth h_(X) is projected by the projection lens 417 through the prism419. This contributes to widen the width of the image W' as shown inFIG. 54.

In FIG. 57, the prism 419 shown in FIG. 55 is shifted in the verticaldirection to come close to the optical axis (H_(Y) =0). As is similar tothe case of FIG. 55, among the lights passing through the prism 419after emanating from a point of the light emitting diode 415 located onthe optical axis, the pencil of light a_(H) passes through the highestpart of the spherical surface of the portion 416 while the pencil oflight a_(L) passes through the lowest part of the spherical surface. Thepencil of light b_(H) passes through the highest part of the sphericalsurface of the portion 416 while the pencil of light b_(L) passesthrough the lowest part of the spherical surface among the lightspassing through the prism 419 after emanating from a point of the lightemitting diode 415 spaced by the distance Y from the optical axis. It isseen that the area on the portion 416 where the lights directed to theprism 419 pass is a little lower than that in FIG. 55.

FIGS. 58A, 58B and 58C show relationship between the position of theprism 19 in the vertical direction relative to the optical axis and theimage W' formed by the projection lens 417 through the prism 419, forexample, at the section I--I in FIG. 53. The image W' moves from theposition of FIG. 58A to the position of FIG. 58C as the position ofprism 419 given by the distance H_(Y) is lowered. The condition of FIG.58A corresponds to the case of FIG. 55 (H_(Y) >0), while the conditionof FIG. 58B to the case of FIG. 57 (H_(Y) =0) and the condition of FIG.58C to the case of H_(Y) <0.

FIG. 59A shows how the effective region on the portion 419 where thelights directed to the prism 419 pass changes due to change in thecenter position D_(o) and the width d_(o) of the prism 419 in thevertical direction, in the model case shown in FIG. 59B. The uppermostlight and the lowestmost light among the lights passing through theprism emanate from the spherical surface of the light condensing portionat positions spaced by R_(max) and R_(min) from the optical axis and theregion defined between R_(max) and R_(min) is the effective region.

FIG. 60A shows relationship between the angle ψ of the prism and thedeflection and θ (see FIG. 60B). The angle ψ the size and the locationof the prism can be determined from the graphs of FIGS. 59A and 60A ifit is determined where the light flux having passed the prism and thelight flux having passed through the parallel plate part of the panelbegin to overlap each other as explained above with reference to FIG.53.

FIG. 61 shows a light projecting optical system of a lighting deviceaccording to a seventh embodiment of the present invention. In thisfigure, 420 and 421 represent light source device and a projection lens,respectively.

A protection panel 422 is provided with a pair of prisms 423 and 424having angles ψ₁ and ψ₂, respectively, as shown. The angle ψ₁ is largerthan the angle ψ₂. FIG. 62 shows an optical path of the light fluxprojected by the light projecting optical syste of FIG. 61. P_(u) andP_(l) indicate the range of spread of the light flux having passedthrough the parallel plate region of the panel 422, while q_(u) andq_(l) indicate the range of spread of the light flux deflected by theprism 423. Further, s_(u) and s_(l) indicate the range of spread of thelight flux deflected by the prism 424. Since the angle ψ₁ of the prism423 is larger than the angle ψ₂ of the prism 424, the light flux havingpassed through the prism 423 is deflected to a larger extent forlighting a nearer distance side that the light flux having passedthrough the prism 424. The sizes of the prism 423 and 424 projected onthe projection lens 421 are shown in FIG. 63. As shown, the area of theupper side prism 424 is larger than the area of the lower prism 424, sothat the light flux having passed through the prism 424 is moreintensive than the light flux having passed through the prism 423. Thisis advantageous because a farther distance range is illuminated byhigher intensity light.

FIG. 64 indicates a cross-section of the light flux projected by theoptical system of FIG. 62 at II--II of FIG. 63. W is an image of thefront spherical portion of the light source device 420 formed by thelight flux (P_(l) ˜P_(u)) having passed through the parallel plate partof protection panel 422, while W' and W" are images of the samespherical portion formed by the light flux (S_(u) ˜S_(l)) and the lightflux (q_(u) ˜q_(l)), respectively. The image W' has the shapecorresponding, for example, to FIG. 58B, and the image W" to FIG. 59A.From the point of view of image brightness, the image W is brightest andthe image W' is brighter than the image W".

Namely, the light projecting optical system of FIG. 61 can provide anillumination light flux which has a large spread in the verticaldirection as a whole and has the sequential intensity distribution ofhigh, intermediate and low intensities from the upper side.

FIG. 65 shows essential parts of a lighting device according to aneighth embodiment of the present invention. In this embodiment, threesmall prisms 435, 436 and 437 having an equal vertex angle(corresponding to ψ in FIGS. 55 and 57) are intermittently formed in thelateral direction on a protection panel arranged in front of aprojection lens 434. If the lateral length of a single prism isshortened in order to weaken the light flux deflected thereby, thephenomenon shown in FIGS. 59A, 59B and 59C also occurs in the lateraldirection, resulting in inconvenience for illumination. However, theintermittent arrangement of the prisms 435, 436 and 437 as shown in FIG.65 not only weakens the light fluxes deflected by the prisms but alsosuppresses occurrence of such a phenomenon.

FIG. 66 shows essential parts of a lighting device according to a ninthembodiment, in which a reflector 438 is used in place of a projectionlens and a discharge bulb 439 is used as a light source in place of alight emitting diode.

FIG. 67 shows a light projecting optical system of a lighting deviceaccording to a tenth embodiment, in which a cylindrical lens 41 isformed on a protection panel 440 in place of a prism. The cylindricallens 41 diverges the light flux incident thereon in such a manner that ashorter distance side is illuminated by higher intensity light. It isalso possible to use an aspherical lens in place of the cylindrical lens441.

In the sixth to tenth embodiments, light deflection means such as aprism and a cylindrical lens is formed on a protection panel but it maybe arranged at a desired position between a light source and aprojecting lens, so long as it can give the spread and intensitydistribution described above.

What is claimed is:
 1. A focus detection system for detecting focuscondition of an objective lens of a camera with respect to an objectwithin a focus detection area which spreads at a solid angle centeringat the optical axis of said objective lens, comprising: a lightprojecting optical system for projecting a flux of light which crossessaid focus detection area at a predetermined angle;means for producing adifference in intensity distribution of said flux of light in apredetermined direction so that said flux of light has a higherintensity at a part thereof to illuminate a farther distance zone withinsaid focus detection area than at a part thereof to illuminate a closerdistance zone within said focus detection area; and a projective patternarranged in said projecting optical system so as to be projected on saidobject as a projective image, said projective pattern having a pluralityof transparent portions and opaque portions alternatively arranged in adirection perpendicular to said predetermined direction.
 2. The focusdetection system of claim 1, wherein said difference producing meansincludes light deflecting means for deflecting a part of said flux oflight towards said closer distance zone.
 3. The focus detection systemof claim 2, further comprising:a light source, wherein said projectivepattern is arranged in a position between said light deflecting meansand said light source.
 4. The focus detection system of claim 1, whereinsaid transparent portions and opaque portions are arranged alternativelyat random pitches.
 5. The focus detection system of claim 1, furthercomprising:an image sensing device provided with a plurality of lightsensing elements, and wherein the arranging direction of saidtransparent and opaque portions are equivalent to that of said lightsensing elements.
 6. An accessory for use with a camera having a focusdetection system for detecting focus condition of an objective lens ofsaid camera with respect to an object within a focus detection areawhich spreads at a solid angle centering at the optical axis of saidobjective lens, said accessory comprising:a light projecting opticalsystem for projecting a flux of light which crosses said focus detectionarea at a predetermined angle; means for producing a difference inintensity distribution of said flux of light in a predetermineddirection so that said flux of light has a higher intensity at a partthereof to illuminate a farther distance zone within said focusdetection area that at a part thereof to illuminate a closer distancezone within said focus detection area; and a projective pattern arrangedin said projecting optical system so as to be projected on said objectas a projective image, said projective pattern having a plurality oftransparent portions and opaque portions alternatively arranged in adirection perpendicular to said predetermined direction.
 7. Theaccessory of claim 6, wherein said difference producing means includeslight deflecting means for deflecting a part of said flux of lighttowards said closer distance zone.
 8. The accessory of claim 7, furthercomprising: a light source, wherein said projective pattern is arrangedin a position between said light deflecting means and said light source.9. The accessory of claim 6, wherein said transparent portions andopaque portions are arranged alternatively at random pitches.
 10. Theaccessory of claim 6, wherein said focus detection system comprises animage sensing device provided with a plurality of light sensing elementsand the arranging direction of said transparent and opaque portions areequivalent to that of said light sensing elements.